Traditional integrated circuit transistor structures rely on the existence of reverse-biased diodes to minimize current leakage from the transistors source, drain, and channel regions to the substrate. Although a reverse-biased diode represents a relatively high resistance current path, there is still significant leakage. A low-resistance current path would be formed if the voltage differential between the substrate and the source/drain regions were to reach the Zener level, at which point avalanche breakdown would occur. Although most integrated circuits operate with voltage differentials far below the Zener level, current leakage at normal operating voltages can still be problematic. In a dynamic random access memory (DRAM), for example, the greater the junction leakage, the more frequent the refresh cycle.
In DRAM memories, the reverse-biased diode formed between the storage node and the substrate can become a low-resistance current path through which the storage node will be partially or completely discharged if an alpha particle of radiation impacts the storage node. Hole-electron pairs are created as the alpha particle traverses the silicon lattice. In a positively charged storage node, the holes (being attracted by the electric field within the junction's depletion region) cross the junction and combine with electrons in the substrate, while the electrons combine with the holes in the positively-charged storage node, depleting the charge.
What is needed is a structure and an uncomplicated process for producing the same which will reduce junction leakage and minimize the effect of alpha particle hits.